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Allow environment variable to control madvise advice. (#7855)

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Introduce experimental support for explicitly specifying the `advice` value provided to `madvise` when releasing the fiber stack.
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Samuel Williams 2023-05-25 11:17:49 +09:00 committed by GitHub
parent 31b28b31fa
commit 492e0025fd
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GPG Key ID: 4AEE18F83AFDEB23
Notes: git 2023-05-25 02:18:10 +00:00 
Merged-By: ioquatix <samuel@codeotaku.com>
1 changed files with 28 additions and 10 deletions
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38
cont.c
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@ -179,7 +179,7 @@ struct fiber_pool {
// A singly-linked list of allocations which contain 1 or more stacks each.
struct fiber_pool_allocation * allocations;
// Provides O(1) stack "allocation":
// Free list that provides O(1) stack "allocation".
struct fiber_pool_vacancy * vacancies;
// The size of the stack allocations (excluding any guard page).
@ -191,13 +191,15 @@ struct fiber_pool {
// The initial number of stacks to allocate.
size_t initial_count;
// Whether to madvise(free) the stack or not:
// Whether to madvise(free) the stack or not.
// If this value is set to 1, the stack will be madvise(free)ed
// (or equivalent), where possible, when it is returned to the pool.
int free_stacks;
// The number of stacks that have been used in this pool.
size_t used;
// The amount to allocate for the vm_stack:
// The amount to allocate for the vm_stack.
size_t vm_stack_size;
};
@ -695,7 +697,9 @@ fiber_pool_stack_free(struct fiber_pool_stack * stack)
// If this is not true, the vacancy information will almost certainly be destroyed:
VM_ASSERT(size <= (stack->size - RB_PAGE_SIZE));
if (DEBUG) fprintf(stderr, "fiber_pool_stack_free: %p+%"PRIuSIZE" [base=%p, size=%"PRIuSIZE"]\n", base, size, stack->base, stack->size);
int advice = stack->pool->free_stacks >> 1;
if (DEBUG) fprintf(stderr, "fiber_pool_stack_free: %p+%"PRIuSIZE" [base=%p, size=%"PRIuSIZE"] advice=%d\n", base, size, stack->base, stack->size, advice);
// The pages being used by the stack can be returned back to the system.
// That doesn't change the page mapping, but it does allow the system to
@ -709,24 +713,29 @@ fiber_pool_stack_free(struct fiber_pool_stack * stack)
#ifdef __wasi__
// WebAssembly doesn't support madvise, so we just don't do anything.
#elif VM_CHECK_MODE > 0 && defined(MADV_DONTNEED)
if (!advice) advice = MADV_DONTNEED;
// This immediately discards the pages and the memory is reset to zero.
madvise(base, size, MADV_DONTNEED);
madvise(base, size, advice);
#elif defined(MADV_FREE_REUSABLE)
if (!advice) advice = MADV_FREE_REUSABLE;
// Darwin / macOS / iOS.
// Acknowledge the kernel down to the task info api we make this
// page reusable for future use.
// As for MADV_FREE_REUSE below we ensure in the rare occasions the task was not
// As for MADV_FREE_REUSABLE below we ensure in the rare occasions the task was not
// completed at the time of the call to re-iterate.
while (madvise(base, size, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN);
while (madvise(base, size, advice) == -1 && errno == EAGAIN);
#elif defined(MADV_FREE)
if (!advice) advice = MADV_FREE;
// Recent Linux.
madvise(base, size, MADV_FREE);
madvise(base, size, advice);
#elif defined(MADV_DONTNEED)
if (!advice) advice = MADV_DONTNEED;
// Old Linux.
madvise(base, size, MADV_DONTNEED);
madvise(base, size, advice);
#elif defined(POSIX_MADV_DONTNEED)
if (!advice) advice = POSIX_MADV_DONTNEED;
// Solaris?
posix_madvise(base, size, POSIX_MADV_DONTNEED);
posix_madvise(base, size, advice);
#elif defined(_WIN32)
VirtualAlloc(base, size, MEM_RESET, PAGE_READWRITE);
// Not available in all versions of Windows.
@ -3439,6 +3448,15 @@ Init_Cont(void)
const char *fiber_shared_fiber_pool_free_stacks = getenv("RUBY_SHARED_FIBER_POOL_FREE_STACKS");
if (fiber_shared_fiber_pool_free_stacks) {
shared_fiber_pool.free_stacks = atoi(fiber_shared_fiber_pool_free_stacks);
if (shared_fiber_pool.free_stacks < 0) {
rb_warn("Setting RUBY_SHARED_FIBER_POOL_FREE_STACKS to a negative value is not allowed.");
shared_fiber_pool.free_stacks = 0;
}
if (shared_fiber_pool.free_stacks > 1) {
rb_warn("Setting RUBY_SHARED_FIBER_POOL_FREE_STACKS to a value greater than 1 is operating system specific, and may cause crashes.");
}
}
rb_cFiber = rb_define_class("Fiber", rb_cObject);